Stabilized diester lubricant



STABILIZED DESTER LUBRICANT Albert W. Lindert, Homewood, llL, assignor to Standard Oil Company, Chicago, 1111., a corporation of iridiana No Drawing. Application October 21, 1954, Serial No. 463,806

6 Claims. (Cl. 25246.7)

This invention relates to a diester synthetic lubricant of improved thermal and oxidation stability.

Specification MiL-L-7808A sets forth properties that must be met by lubricants for jet engines, gas turbines, aircraft, etc. including rigid viscosity requirements at 210 F. and -65 F., low temperature storage stability, oxidation-corrosion resistance, evaporation loss at 400 F., a 10,000 R. P. M. gear test and a panel-coking test conducted at 600 F. These requirements are met by certain diester synthetic lubricants such, for example, as dioctyl sebacate, azelate and/or adipate containing about percent tricresyl phosphate, about .5 percent phenothiazine with or without a viscosity index improver. However, when such compositions are employed as lubricants for moving parts operating at close clearances and/or carrying heavy loads at high temperatures, they are subject to undesirable oxidation and/or thermal degradation which may result in seizure of moving parts. An object of this invention is to provide an improved diester synthetic lubricant which not only meets the MIL-L-7808A specification (except for possible corrosion requirements on certain metals under certain conditions) but which is of improved stability with respect to oxidation and thermal degradation. Another object is to provide such a lubricant which gives less coke deposit in the 600 F. panel-coking test. A further object is to provide a lubricant of a higher load carrying capacity, particularly as a gear lubricant operating at high temperature. Other objects will be apparent as the detailed description of the invention proceeds.

It has been found that a lubricant which meets most of the MIL-L-7808A requirements and, at the same time, possesses outstanding stability against oxidation and thermal degradation can be obtained by adding to a suitable base fluid dilauryl selenide in amounts of about .5 to 5 percent, preferably about 2 percent. An example of the new lubricant composition is as follows:

92.5% dioctyl azelate 5 tricresyl phosphate .5 phenothiazine 2% dilauryl selenide Instead of dioctyl azelate I may use diisooctyl adipate, or a mixture of the adipate with azelate in any desired proportions. The diester component is preferably employed in amounts in the range of 90 to 95 percent and, while the octyl esters are preferred, other diesters may be employed, said diesters preferably being of dicarboxylic acids containing about 4 to 8 carbon atoms, the added ester groups each having a chain length of about 5 to 15 carbon atoms. The tricresyl phosphate may be employed in amounts of about 4 to 6 percent and this component may be replaced by other organic phosphates of similar properties. The phenotiazine may be employed in amounts ranging from about .3 to .7 percent. As above stated, the dilauryl 7 selenide is preferably employed in amounts of about 2. percent or in the range of about .5 to 5 percent and other 2,792,346 Patented May 14, 1957 organic selenides of approximately the same carbon chain length as the dilauryl selenide may be used.

The lubricant may be prepared by simply mixing the components at a temperature in the range of about 100 to 150 F. Alternately, the dilauryl selenide may be warmed to its melting point and admixed in the described amount with a previously formed diester lubricant.

The remarkable stabilizing eflect of the added dilauryl selenide is shown by the results of 600 F. panel-coking tests made on a base fluid containing 94.5 percent dioctyl azelate, 5 percent tricresyl phosphate and .5 percent phenothiazine with the following results:

From the above test data it will be seen that the dilauryl selenide reduced the coke deposit to about one-fourth the level obtained in the absence of stabilizer. Tributyl tin, which might be expected to have a similar result, actually gives about five times as much coke deposit as the base fluid.

The lubricant composition described in the foregoing example was tested for lubricating the plungers and bushings of a high temperature pump on a jet engine and found to increase by about three times the length of running obtainable with the base lubricant in the absence of the dilauryl selenide. The high temperature in this case was a 200 to 300 F. oil sump temperature but, with close clearances and high speed operation, the actual temperature of the oil between movmg parts was probably much higher. Although the dilauryl selenide-containing lubricant is slightly corrosive to silver and copper under high temperature test conditions, no corrosion problem was apparent in the test on the jet pump.

lt is believed that dilauryl selenide is substantially nontoxic as opposed to the organic selenides which are quite poisonous; however, it is recommended that adequate safety precautions be employed in handling this material, particularly when it is subjected to high temperatures.

I claim:

1. A lubricant consisting essentially of about to percent of a diester of a dicarboxylic acid containing about 4 to 8 carbon atoms per molecule, the added ester groups having a carbon chain length of about 5 to 15 carbon atoms, about 4 to 6 percent tricresyl phosphate, about .3 to .7 percent phenothiazine and about .5 to 5 weight percent dilauryl selenide.

2. The lubricant of claim 1 wherein at least a part of the diester is diisooctyl adipate.

3. The lubricant of claim 1 wherein at least a part of the diester is dioctyl azelate.

4. The lubricant of claim 1 wherein the diester is a mixture of diisooctyl adipate and dioctyl azelate.

5. A lubricant consisting essentially of a diester of a dicarboxylic acid containing about 4 to 8 carbon atoms, the added ester groups having a chain length of about 5 to 15 carbon atoms, about 5 weight percent of tricresyl phosphate, about .5 weight percent phenothiazine and about 2 percent dilauryl selenide.

6. A lubricant having approximately the following composition: 92.5 percent dioctyl azelate, 5 percent tricresyl phosphate, .5 percent phenothiazine, and 2 percent dilauryl selenide.

References Cited in the file of this patent UNITED STATES PATENTS 2,167,867 Benning Aug. 1, 1939 2,190,648 Cantrell Feb. 20, 1940 2,398,415 Denison Apr. 16, 1946 

1. A LUBRICANT CONSISTING ESSENTIALLY OF ABOUT 90 TO 95 PERCENT OF A DIESTER OF A DICARBOXYLIC ACID CONTAINING ABOUT 4 TO 8 CARBON ATOMS PER MOLECULE, THE ADDED ESTER GROUPS HAVING A CARBON CHAIN LENGTH OF ABOUT 5 TO 15 CARBON ATOMS, ABOUT 4 TO 6 PERCENT TRICRESYL PHOSPHATE, ABOUT 3 TO 7 PERCENT PHENOTHIAZINE AND ABOUT 5 TO 5 WEIGHT PERCENT DILAURYL SELEMIDE. 